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perlport

PERLPORT(1)	       Perl Programmers Reference Guide 	   PERLPORT(1)



NAME
       perlport - Writing portable Perl

DESCRIPTION
       Perl runs on numerous operating systems.  While most of them share much
       in common, they also have their own unique features.

       This document is meant to help you to find out what constitutes porta-
       ble Perl code.  That way once you make a decision to write portably,
       you know where the lines are drawn, and you can stay within them.

       There is a tradeoff between taking full advantage of one particular
       type of computer and taking advantage of a full range of them.  Natu-
       rally, as you broaden your range and become more diverse, the common
       factors drop, and you are left with an increasingly smaller area of
       common ground in which you can operate to accomplish a particular task.
       Thus, when you begin attacking a problem, it is important to consider
       under which part of the tradeoff curve you want to operate.  Specifi-
       cally, you must decide whether it is important that the task that you
       are coding have the full generality of being portable, or whether to
       just get the job done right now.  This is the hardest choice to be
       made.  The rest is easy, because Perl provides many choices, whichever
       way you want to approach your problem.

       Looking at it another way, writing portable code is usually about will-
       fully limiting your available choices.  Naturally, it takes discipline
       and sacrifice to do that.  The product of portability and convenience
       may be a constant.  You have been warned.

       Be aware of two important points:

       Not all Perl programs have to be portable
	   There is no reason you should not use Perl as a language to glue
	   Unix tools together, or to prototype a Macintosh application, or to
	   manage the Windows registry.  If it makes no sense to aim for
	   portability for one reason or another in a given program, then
	   don't bother.

       Nearly all of Perl already is portable
	   Don't be fooled into thinking that it is hard to create portable
	   Perl code.  It isn't.  Perl tries its level-best to bridge the gaps
	   between what's available on different platforms, and all the means
	   available to use those features.  Thus almost all Perl code runs on
	   any machine without modification.  But there are some significant
	   issues in writing portable code, and this document is entirely
	   about those issues.

       Here's the general rule: When you approach a task commonly done using a
       whole range of platforms, think about writing portable code.  That way,
       you don't sacrifice much by way of the implementation choices you can
       avail yourself of, and at the same time you can give your users lots of
       platform choices.  On the other hand, when you have to take advantage
       of some unique feature of a particular platform, as is often the case
       with systems programming (whether for Unix, Windows, Mac OS, VMS,
       etc.), consider writing platform-specific code.

       When the code will run on only two or three operating systems, you may
       need to consider only the differences of those particular systems.  The
       important thing is to decide where the code will run and to be deliber-
       ate in your decision.

       The material below is separated into three main sections: main issues
       of portability ("ISSUES"), platform-specific issues ("PLATFORMS"), and
       built-in perl functions that behave differently on various ports
       ("FUNCTION IMPLEMENTATIONS").

       This information should not be considered complete; it includes possi-
       bly transient information about idiosyncrasies of some of the ports,
       almost all of which are in a state of constant evolution.  Thus, this
       material should be considered a perpetual work in progress ("").

ISSUES
       Newlines

       In most operating systems, lines in files are terminated by newlines.
       Just what is used as a newline may vary from OS to OS.  Unix tradition-
       ally uses "\012", one type of DOSish I/O uses "\015\012", and Mac OS
       uses "\015".

       Perl uses "\n" to represent the "logical" newline, where what is logi-
       cal may depend on the platform in use.  In MacPerl, "\n" always means
       "\015".	In DOSish perls, "\n" usually means "\012", but when accessing
       a file in "text" mode, STDIO translates it to (or from) "\015\012",
       depending on whether you're reading or writing.	Unix does the same
       thing on ttys in canonical mode.  "\015\012" is commonly referred to as
       CRLF.

       A common cause of unportable programs is the misuse of chop() to trim
       newlines:

	   # XXX UNPORTABLE!
	   while() {
	       chop;
	       @array = split(/:/);
	       #...
	   }

       You can get away with this on Unix and Mac OS (they have a single char-
       acter end-of-line), but the same program will break under DOSish perls
       because you're only chop()ing half the end-of-line.  Instead, chomp()
       should be used to trim newlines.  The Dunce::Files module can help
       audit your code for misuses of chop().

       When dealing with binary files (or text files in binary mode) be sure
       to explicitly set $/ to the appropriate value for your file format
       before using chomp().

       Because of the "text" mode translation, DOSish perls have limitations
       in using "seek" and "tell" on a file accessed in "text" mode.  Stick to
       "seek"-ing to locations you got from "tell" (and no others), and you
       are usually free to use "seek" and "tell" even in "text" mode.  Using
       "seek" or "tell" or other file operations may be non-portable.  If you
       use "binmode" on a file, however, you can usually "seek" and "tell"
       with arbitrary values in safety.

       A common misconception in socket programming is that "\n" eq "\012"
       everywhere.  When using protocols such as common Internet protocols,
       "\012" and "\015" are called for specifically, and the values of the
       logical "\n" and "\r" (carriage return) are not reliable.

	   print SOCKET "Hi there, client!\r\n";      # WRONG
	   print SOCKET "Hi there, client!\015\012";  # RIGHT

       However, using "\015\012" (or "\cM\cJ", or "\x0D\x0A") can be tedious
       and unsightly, as well as confusing to those maintaining the code.  As
       such, the Socket module supplies the Right Thing for those who want it.

	   use Socket qw(:DEFAULT :crlf);
	   print SOCKET "Hi there, client!$CRLF"      # RIGHT

       When reading from a socket, remember that the default input record sep-
       arator $/ is "\n", but robust socket code will recognize as either
       "\012" or "\015\012" as end of line:

	   while () {
	       # ...
	   }

       Because both CRLF and LF end in LF, the input record separator can be
       set to LF and any CR stripped later.  Better to write:

	   use Socket qw(:DEFAULT :crlf);
	   local($/) = LF;	# not needed if $/ is already \012

	   while () {
	       s/$CR?$LF/\n/;	# not sure if socket uses LF or CRLF, OK
	   #   s/\015?\012/\n/; # same thing
	   }

       This example is preferred over the previous one--even for Unix plat-
       forms--because now any "\015"'s ("\cM"'s) are stripped out (and there
       was much rejoicing).

       Similarly, functions that return text data--such as a function that
       fetches a web page--should sometimes translate newlines before return-
       ing the data, if they've not yet been translated to the local newline
       representation.	A single line of code will often suffice:

	   $data =~ s/\015?\012/\n/g;
	   return $data;

       Some of this may be confusing.  Here's a handy reference to the ASCII
       CR and LF characters.  You can print it out and stick it in your wal-
       let.

	   LF  eq  \012  eq  \x0A  eq  \cJ  eq	chr(10)  eq  ASCII 10
	   CR  eq  \015  eq  \x0D  eq  \cM  eq	chr(13)  eq  ASCII 13

		    | Unix | DOS  | Mac  |
	       ---------------------------
	       \n   |  LF  |  LF  |  CR  |
	       \r   |  CR  |  CR  |  LF  |
	       \n * |  LF  | CRLF |  CR  |
	       \r * |  CR  |  CR  |  LF  |
	       ---------------------------
	       * text-mode STDIO

       The Unix column assumes that you are not accessing a serial line (like
       a tty) in canonical mode.  If you are, then CR on input becomes "\n",
       and "\n" on output becomes CRLF.

       These are just the most common definitions of "\n" and "\r" in Perl.
       There may well be others.  For example, on an EBCDIC implementation
       such as z/OS (OS/390) or OS/400 (using the ILE, the PASE is
       ASCII-based) the above material is similar to "Unix" but the code num-
       bers change:

	   LF  eq  \025  eq  \x15  eq  \cU  eq	chr(21)  eq  CP-1047 21
	   LF  eq  \045  eq  \x25  eq		chr(37)  eq  CP-0037 37
	   CR  eq  \015  eq  \x0D  eq  \cM  eq	chr(13)  eq  CP-1047 13
	   CR  eq  \015  eq  \x0D  eq  \cM  eq	chr(13)  eq  CP-0037 13

		    | z/OS | OS/400 |
	       ----------------------
	       \n   |  LF  |  LF    |
	       \r   |  CR  |  CR    |
	       \n * |  LF  |  LF    |
	       \r * |  CR  |  CR    |
	       ----------------------
	       * text-mode STDIO

       Numbers endianness and Width

       Different CPUs store integers and floating point numbers in different
       orders (called endianness) and widths (32-bit and 64-bit being the most
       common today).  This affects your programs when they attempt to trans-
       fer numbers in binary format from one CPU architecture to another, usu-
       ally either "live" via network connection, or by storing the numbers to
       secondary storage such as a disk file or tape.

       Conflicting storage orders make utter mess out of the numbers.  If a
       little-endian host (Intel, VAX) stores 0x12345678 (305419896 in deci-
       mal), a big-endian host (Motorola, Sparc, PA) reads it as 0x78563412
       (2018915346 in decimal).  Alpha and MIPS can be either: Digital/Compaq
       used/uses them in little-endian mode; SGI/Cray uses them in big-endian
       mode.  To avoid this problem in network (socket) connections use the
       "pack" and "unpack" formats "n" and "N", the "network" orders.  These
       are guaranteed to be portable.

       As of perl 5.8.5, you can also use the ">" and "<" modifiers to force
       big- or little-endian byte-order.  This is useful if you want to store
       signed integers or 64-bit integers, for example.

       You can explore the endianness of your platform by unpacking a data
       structure packed in native format such as:

	   print unpack("h*", pack("s2", 1, 2)), "\n";
	   # '10002000' on e.g. Intel x86 or Alpha 21064 in little-endian mode
	   # '00100020' on e.g. Motorola 68040

       If you need to distinguish between endian architectures you could use
       either of the variables set like so:

	   $is_big_endian   = unpack("h*", pack("s", 1)) =~ /01/;
	   $is_little_endian = unpack("h*", pack("s", 1)) =~ /^1/;

       Differing widths can cause truncation even between platforms of equal
       endianness.  The platform of shorter width loses the upper parts of the
       number.	There is no good solution for this problem except to avoid
       transferring or storing raw binary numbers.

       One can circumnavigate both these problems in two ways.	Either trans-
       fer and store numbers always in text format, instead of raw binary, or
       else consider using modules like Data::Dumper (included in the standard
       distribution as of Perl 5.005) and Storable (included as of perl 5.8).
       Keeping all data as text significantly simplifies matters.

       The v-strings are portable only up to v2147483647 (0x7FFFFFFF), that's
       how far EBCDIC, or more precisely UTF-EBCDIC will go.

       Files and Filesystems

       Most platforms these days structure files in a hierarchical fashion.
       So, it is reasonably safe to assume that all platforms support the
       notion of a "path" to uniquely identify a file on the system.  How that
       path is really written, though, differs considerably.

       Although similar, file path specifications differ between Unix, Win-
       dows, Mac OS, OS/2, VMS, VOS, RISC OS, and probably others.  Unix, for
       example, is one of the few OSes that has the elegant idea of a single
       root directory.

       DOS, OS/2, VMS, VOS, and Windows can work similarly to Unix with "/" as
       path separator, or in their own idiosyncratic ways (such as having sev-
       eral root directories and various "unrooted" device files such NIL: and
       LPT:).

       Mac OS uses ":" as a path separator instead of "/".

       The filesystem may support neither hard links ("link") nor symbolic
       links ("symlink", "readlink", "lstat").

       The filesystem may support neither access timestamp nor change time-
       stamp (meaning that about the only portable timestamp is the modifica-
       tion timestamp), or one second granularity of any timestamps (e.g. the
       FAT filesystem limits the time granularity to two seconds).

       The "inode change timestamp" (the "-C" filetest) may really be the
       "creation timestamp" (which it is not in UNIX).

       VOS perl can emulate Unix filenames with "/" as path separator.	The
       native pathname characters greater-than, less-than, number-sign, and
       percent-sign are always accepted.

       RISC OS perl can emulate Unix filenames with "/" as path separator, or
       go native and use "." for path separator and ":" to signal filesystems
       and disk names.

       Don't assume UNIX filesystem access semantics: that read, write, and
       execute are all the permissions there are, and even if they exist, that
       their semantics (for example what do r, w, and x mean on a directory)
       are the UNIX ones.  The various UNIX/POSIX compatibility layers usually
       try to make interfaces like chmod() work, but sometimes there simply is
       no good mapping.

       If all this is intimidating, have no (well, maybe only a little) fear.
       There are modules that can help.  The File::Spec modules provide meth-
       ods to do the Right Thing on whatever platform happens to be running
       the program.

	   use File::Spec::Functions;
	   chdir(updir());	  # go up one directory
	   $file = catfile(curdir(), 'temp', 'file.txt');
	   # on Unix and Win32, './temp/file.txt'
	   # on Mac OS, ':temp:file.txt'
	   # on VMS, '[.temp]file.txt'

       File::Spec is available in the standard distribution as of version
       5.004_05.  File::Spec::Functions is only in File::Spec 0.7 and later,
       and some versions of perl come with version 0.6.  If File::Spec is not
       updated to 0.7 or later, you must use the object-oriented interface
       from File::Spec (or upgrade File::Spec).

       In general, production code should not have file paths hardcoded.  Mak-
       ing them user-supplied or read from a configuration file is better,
       keeping in mind that file path syntax varies on different machines.

       This is especially noticeable in scripts like Makefiles and test
       suites, which often assume "/" as a path separator for subdirectories.

       Also of use is File::Basename from the standard distribution, which
       splits a pathname into pieces (base filename, full path to directory,
       and file suffix).

       Even when on a single platform (if you can call Unix a single plat-
       form), remember not to count on the existence or the contents of par-
       ticular system-specific files or directories, like /etc/passwd,
       /etc/sendmail.conf, /etc/resolv.conf, or even /tmp/.  For example,
       /etc/passwd may exist but not contain the encrypted passwords, because
       the system is using some form of enhanced security.  Or it may not con-
       tain all the accounts, because the system is using NIS.	If code does
       need to rely on such a file, include a description of the file and its
       format in the code's documentation, then make it easy for the user to
       override the default location of the file.

       Don't assume a text file will end with a newline.  They should, but
       people forget.

       Do not have two files or directories of the same name with different
       case, like test.pl and Test.pl, as many platforms have case-insensitive
       (or at least case-forgiving) filenames.	Also, try not to have non-word
       characters (except for ".") in the names, and keep them to the 8.3 con-
       vention, for maximum portability, onerous a burden though this may
       appear.

       Likewise, when using the AutoSplit module, try to keep your functions
       to 8.3 naming and case-insensitive conventions; or, at the least, make
       it so the resulting files have a unique (case-insensitively) first 8
       characters.

       Whitespace in filenames is tolerated on most systems, but not all, and
       even on systems where it might be tolerated, some utilities might
       become confused by such whitespace.

       Many systems (DOS, VMS) cannot have more than one "." in their file-
       names.

       Don't assume ">" won't be the first character of a filename.  Always
       use "<" explicitly to open a file for reading, or even better, use the
       three-arg version of open, unless you want the user to be able to spec-
       ify a pipe open.

	   open(FILE, '<', $existing_file) or die $!;

       If filenames might use strange characters, it is safest to open it with
       "sysopen" instead of "open".  "open" is magic and can translate charac-
       ters like ">", "<", and "|", which may be the wrong thing to do.
       (Sometimes, though, it's the right thing.)  Three-arg open can also
       help protect against this translation in cases where it is undesirable.

       Don't use ":" as a part of a filename since many systems use that for
       their own semantics (Mac OS Classic for separating pathname components,
       many networking schemes and utilities for separating the nodename and
       the pathname, and so on).  For the same reasons, avoid "@", ";" and
       "|".

       Don't assume that in pathnames you can collapse two leading slashes
       "//" into one: some networking and clustering filesystems have special
       semantics for that.  Let the operating system to sort it out.

       The portable filename characters as defined by ANSI C are

	a b c d e f g h i j k l m n o p q r t u v w x y z
	A B C D E F G H I J K L M N O P Q R T U V W X Y Z
	0 1 2 3 4 5 6 7 8 9
	. _ -

       and the "-" shouldn't be the first character.  If you want to be hyper-
       correct, stay case-insensitive and within the 8.3 naming convention
       (all the files and directories have to be unique within one directory
       if their names are lowercased and truncated to eight characters before
       the ".", if any, and to three characters after the ".", if any).  (And
       do not use "."s in directory names.)

       System Interaction

       Not all platforms provide a command line.  These are usually platforms
       that rely primarily on a Graphical User Interface (GUI) for user inter-
       action.	A program requiring a command line interface might not work
       everywhere.  This is probably for the user of the program to deal with,
       so don't stay up late worrying about it.

       Some platforms can't delete or rename files held open by the system,
       this limitation may also apply to changing filesystem metainformation
       like file permissions or owners.  Remember to "close" files when you
       are done with them.  Don't "unlink" or "rename" an open file.  Don't
       "tie" or "open" a file already tied or opened; "untie" or "close" it
       first.

       Don't open the same file more than once at a time for writing, as some
       operating systems put mandatory locks on such files.

       Don't assume that write/modify permission on a directory gives the
       right to add or delete files/directories in that directory.  That is
       filesystem specific: in some filesystems you need write/modify permis-
       sion also (or even just) in the file/directory itself.  In some
       filesystems (AFS, DFS) the permission to add/delete directory entries
       is a completely separate permission.

       Don't assume that a single "unlink" completely gets rid of the file:
       some filesystems (most notably the ones in VMS) have versioned filesys-
       tems, and unlink() removes only the most recent one (it doesn't remove
       all the versions because by default the native tools on those platforms
       remove just the most recent version, too).  The portable idiom to
       remove all the versions of a file is

	   1 while unlink "file";

       This will terminate if the file is undeleteable for some reason (pro-
       tected, not there, and so on).

       Don't count on a specific environment variable existing in %ENV.  Don't
       count on %ENV entries being case-sensitive, or even case-preserving.
       Don't try to clear %ENV by saying "%ENV = ();", or, if you really have
       to, make it conditional on "$^O ne 'VMS'" since in VMS the %ENV table
       is much more than a per-process key-value string table.

       Don't count on signals or %SIG for anything.

       Don't count on filename globbing.  Use "opendir", "readdir", and
       "closedir" instead.

       Don't count on per-program environment variables, or per-program cur-
       rent directories.

       Don't count on specific values of $!, neither numeric nor especially
       the strings values-- users may switch their locales causing error mes-
       sages to be translated into their languages.  If you can trust a POSIX-
       ish environment, you can portably use the symbols defined by the Errno
       module, like ENOENT.  And don't trust on the values of $!  at all
       except immediately after a failed system call.

       Command names versus file pathnames

       Don't assume that the name used to invoke a command or program with
       "system" or "exec" can also be used to test for the existence of the
       file that holds the executable code for that command or program.
       First, many systems have "internal" commands that are built-in to the
       shell or OS and while these commands can be invoked, there is no corre-
       sponding file.  Second, some operating systems (e.g., Cygwin, DJGPP,
       OS/2, and VOS) have required suffixes for executable files; these suf-
       fixes are generally permitted on the command name but are not required.
       Thus, a command like "perl" might exist in a file named "perl",
       "perl.exe", or "perl.pm", depending on the operating system.  The vari-
       able "_exe" in the Config module holds the executable suffix, if any.
       Third, the VMS port carefully sets up $^X and $Config{perlpath} so that
       no further processing is required.  This is just as well, because the
       matching regular expression used below would then have to deal with a
       possible trailing version number in the VMS file name.

       To convert $^X to a file pathname, taking account of the requirements
       of the various operating system possibilities, say:

	 use Config;
	 $thisperl = $^X;
	 if ($^O ne 'VMS')
	    {$thisperl .= $Config{_exe} unless $thisperl =~ m/$Config{_exe}$/i;}

       To convert $Config{perlpath} to a file pathname, say:

	 use Config;
	 $thisperl = $Config{perlpath};
	 if ($^O ne 'VMS')
	    {$thisperl .= $Config{_exe} unless $thisperl =~ m/$Config{_exe}$/i;}

       Networking

       Don't assume that you can reach the public Internet.

       Don't assume that there is only one way to get through firewalls to the
       public Internet.

       Don't assume that you can reach outside world through any other port
       than 80, or some web proxy.  ftp is blocked by many firewalls.

       Don't assume that you can send email by connecting to the local SMTP
       port.

       Don't assume that you can reach yourself or any node by the name
       'localhost'.  The same goes for '127.0.0.1'.  You will have to try
       both.

       Don't assume that the host has only one network card, or that it can't
       bind to many virtual IP addresses.

       Don't assume a particular network device name.

       Don't assume a particular set of ioctl()s will work.

       Don't assume that you can ping hosts and get replies.

       Don't assume that any particular port (service) will respond.

       Don't assume that Sys::Hostname (or any other API or command) returns
       either a fully qualified hostname or a non-qualified hostname: it all
       depends on how the system had been configured.  Also remember things
       like DHCP and NAT-- the hostname you get back might not be very useful.

       All the above "don't":s may look daunting, and they are -- but the key
       is to degrade gracefully if one cannot reach the particular network
       service one wants.  Croaking or hanging do not look very professional.

       Interprocess Communication (IPC)

       In general, don't directly access the system in code meant to be porta-
       ble.  That means, no "system", "exec", "fork", "pipe", ``, "qx//",
       "open" with a "|", nor any of the other things that makes being a perl
       hacker worth being.

       Commands that launch external processes are generally supported on most
       platforms (though many of them do not support any type of forking).
       The problem with using them arises from what you invoke them on.
       External tools are often named differently on different platforms, may
       not be available in the same location, might accept different argu-
       ments, can behave differently, and often present their results in a
       platform-dependent way.	Thus, you should seldom depend on them to pro-
       duce consistent results. (Then again, if you're calling netstat -a, you
       probably don't expect it to run on both Unix and CP/M.)

       One especially common bit of Perl code is opening a pipe to sendmail:

	   open(MAIL, '|/usr/lib/sendmail -t')
	       or die "cannot fork sendmail: $!";

       This is fine for systems programming when sendmail is known to be
       available.  But it is not fine for many non-Unix systems, and even some
       Unix systems that may not have sendmail installed.  If a portable solu-
       tion is needed, see the various distributions on CPAN that deal with
       it.  Mail::Mailer and Mail::Send in the MailTools distribution are com-
       monly used, and provide several mailing methods, including mail, send-
       mail, and direct SMTP (via Net::SMTP) if a mail transfer agent is not
       available.  Mail::Sendmail is a standalone module that provides simple,
       platform-independent mailing.

       The Unix System V IPC ("msg*(), sem*(), shm*()") is not available even
       on all Unix platforms.

       Do not use either the bare result of "pack("N", 10, 20, 30, 40)" or
       bare v-strings (such as "v10.20.30.40") to represent IPv4 addresses:
       both forms just pack the four bytes into network order.	That this
       would be equal to the C language "in_addr" struct (which is what the
       socket code internally uses) is not guaranteed.	To be portable use the
       routines of the Socket extension, such as "inet_aton()", "inet_ntoa()",
       and "sockaddr_in()".

       The rule of thumb for portable code is: Do it all in portable Perl, or
       use a module (that may internally implement it with platform-specific
       code, but expose a common interface).

       External Subroutines (XS)

       XS code can usually be made to work with any platform, but dependent
       libraries, header files, etc., might not be readily available or porta-
       ble, or the XS code itself might be platform-specific, just as Perl
       code might be.  If the libraries and headers are portable, then it is
       normally reasonable to make sure the XS code is portable, too.

       A different type of portability issue arises when writing XS code:
       availability of a C compiler on the end-user's system.  C brings with
       it its own portability issues, and writing XS code will expose you to
       some of those.  Writing purely in Perl is an easier way to achieve
       portability.

       Standard Modules

       In general, the standard modules work across platforms.	Notable excep-
       tions are the CPAN module (which currently makes connections to exter-
       nal programs that may not be available), platform-specific modules
       (like ExtUtils::MM_VMS), and DBM modules.

       There is no one DBM module available on all platforms.  SDBM_File and
       the others are generally available on all Unix and DOSish ports, but
       not in MacPerl, where only NBDM_File and DB_File are available.

       The good news is that at least some DBM module should be available, and
       AnyDBM_File will use whichever module it can find.  Of course, then the
       code needs to be fairly strict, dropping to the greatest common factor
       (e.g., not exceeding 1K for each record), so that it will work with any
       DBM module.  See AnyDBM_File for more details.

       Time and Date

       The system's notion of time of day and calendar date is controlled in
       widely different ways.  Don't assume the timezone is stored in
       $ENV{TZ}, and even if it is, don't assume that you can control the
       timezone through that variable.	Don't assume anything about the three-
       letter timezone abbreviations (for example that MST would be the Moun-
       tain Standard Time, it's been known to stand for Moscow Standard Time).
       If you need to use timezones, express them in some unambiguous format
       like the exact number of minutes offset from UTC, or the POSIX timezone
       format.

       Don't assume that the epoch starts at 00:00:00, January 1, 1970,
       because that is OS- and implementation-specific.  It is better to store
       a date in an unambiguous representation.  The ISO 8601 standard defines
       YYYY-MM-DD as the date format, or YYYY-MM-DDTHH-MM-SS (that's a literal
       "T" separating the date from the time).	Please do use the ISO 8601
       instead of making us to guess what date 02/03/04 might be.  ISO 8601
       even sorts nicely as-is.  A text representation (like "1987-12-18") can
       be easily converted into an OS-specific value using a module like
       Date::Parse.  An array of values, such as those returned by "local-
       time", can be converted to an OS-specific representation using
       Time::Local.

       When calculating specific times, such as for tests in time or date mod-
       ules, it may be appropriate to calculate an offset for the epoch.

	   require Time::Local;
	   $offset = Time::Local::timegm(0, 0, 0, 1, 0, 70);

       The value for $offset in Unix will be 0, but in Mac OS will be some
       large number.  $offset can then be added to a Unix time value to get
       what should be the proper value on any system.

       On Windows (at least), you shouldn't pass a negative value to "gmtime"
       or "localtime".

       Character sets and character encoding

       Assume very little about character sets.

       Assume nothing about numerical values ("ord", "chr") of characters.  Do
       not use explicit code point ranges (like \xHH-\xHH); use for example
       symbolic character classes like "[:print:]".

       Do not assume that the alphabetic characters are encoded contiguously
       (in the numeric sense).	There may be gaps.

       Do not assume anything about the ordering of the characters.  The low-
       ercase letters may come before or after the uppercase letters; the low-
       ercase and uppercase may be interlaced so that both "a" and "A" come
       before "b"; the accented and other international characters may be
       interlaced so that ae comes before "b".

       Internationalisation

       If you may assume POSIX (a rather large assumption), you may read more
       about the POSIX locale system from perllocale.  The locale system at
       least attempts to make things a little bit more portable, or at least
       more convenient and native-friendly for non-English users.  The system
       affects character sets and encoding, and date and time format-
       ting--amongst other things.

       If you really want to be international, you should consider Unicode.
       See perluniintro and perlunicode for more information.

       If you want to use non-ASCII bytes (outside the bytes 0x00..0x7f) in
       the "source code" of your code, to be portable you have to be explicit
       about what bytes they are.  Someone might for example be using your
       code under a UTF-8 locale, in which case random native bytes might be
       illegal ("Malformed UTF-8 ...")	This means that for example embedding
       ISO 8859-1 bytes beyond 0x7f into your strings might cause trouble
       later.  If the bytes are native 8-bit bytes, you can use the "bytes"
       pragma.	If the bytes are in a string (regular expression being a curi-
       ous string), you can often also use the "\xHH" notation instead of
       embedding the bytes as-is.  If they are in some particular legacy
       encoding (ether single-byte or something more complicated), you can use
       the "encoding" pragma.  (If you want to write your code in UTF-8, you
       can use either the "utf8" pragma, or the "encoding" pragma.)  The
       "bytes" and "utf8" pragmata are available since Perl 5.6.0, and the
       "encoding" pragma since Perl 5.8.0.

       System Resources

       If your code is destined for systems with severely constrained (or
       missing!) virtual memory systems then you want to be especially mindful
       of avoiding wasteful constructs such as:

	   # NOTE: this is no longer "bad" in perl5.005
	   for (0..10000000) {} 		      # bad
	   for (my $x = 0; $x <= 10000000; ++$x) {}   # good

	   @lines = ;		      # bad

	   while () {$file .= $_} 	      # sometimes bad
	   $file = join('', );		      # better

       The last two constructs may appear unintuitive to most people.  The
       first repeatedly grows a string, whereas the second allocates a large
       chunk of memory in one go.  On some systems, the second is more effi-
       cient that the first.

       Security

       Most multi-user platforms provide basic levels of security, usually
       implemented at the filesystem level.  Some, however, do not-- unfortu-
       nately.	Thus the notion of user id, or "home" directory, or even the
       state of being logged-in, may be unrecognizable on many platforms.  If
       you write programs that are security-conscious, it is usually best to
       know what type of system you will be running under so that you can
       write code explicitly for that platform (or class of platforms).

       Don't assume the UNIX filesystem access semantics: the operating system
       or the filesystem may be using some ACL systems, which are richer lan-
       guages than the usual rwx.  Even if the rwx exist, their semantics
       might be different.

       (From security viewpoint testing for permissions before attempting to
       do something is silly anyway: if one tries this, there is potential for
       race conditions-- someone or something might change the permissions
       between the permissions check and the actual operation.	Just try the
       operation.)

       Don't assume the UNIX user and group semantics: especially, don't
       expect the $< and $> (or the $( and $)) to work for switching identi-
       ties (or memberships).

       Don't assume set-uid and set-gid semantics. (And even if you do, think
       twice: set-uid and set-gid are a known can of security worms.)

       Style

       For those times when it is necessary to have platform-specific code,
       consider keeping the platform-specific code in one place, making port-
       ing to other platforms easier.  Use the Config module and the special
       variable $^O to differentiate platforms, as described in "PLATFORMS".

       Be careful in the tests you supply with your module or programs.  Mod-
       ule code may be fully portable, but its tests might not be.  This often
       happens when tests spawn off other processes or call external programs
       to aid in the testing, or when (as noted above) the tests assume cer-
       tain things about the filesystem and paths.  Be careful not to depend
       on a specific output style for errors, such as when checking $! after a
       failed system call.  Using $! for anything else than displaying it as
       output is doubtful (though see the Errno module for testing reasonably
       portably for error value). Some platforms expect a certain output for-
       mat, and Perl on those platforms may have been adjusted accordingly.
       Most specifically, don't anchor a regex when testing an error value.

CPAN Testers
       Modules uploaded to CPAN are tested by a variety of volunteers on dif-
       ferent platforms.  These CPAN testers are notified by mail of each new
       upload, and reply to the list with PASS, FAIL, NA (not applicable to
       this platform), or UNKNOWN (unknown), along with any relevant nota-
       tions.

       The purpose of the testing is twofold: one, to help developers fix any
       problems in their code that crop up because of lack of testing on other
       platforms; two, to provide users with information about whether a given
       module works on a given platform.

       Also see:

       o   Mailing list: cpan-testers@perl.org

       o   Testing results: http://testers.cpan.org/

PLATFORMS
       As of version 5.002, Perl is built with a $^O variable that indicates
       the operating system it was built on.  This was implemented to help
       speed up code that would otherwise have to "use Config" and use the
       value of $Config{osname}.  Of course, to get more detailed information
       about the system, looking into %Config is certainly recommended.

       %Config cannot always be trusted, however, because it was built at com-
       pile time.  If perl was built in one place, then transferred elsewhere,
       some values may be wrong.  The values may even have been edited after
       the fact.

       Unix

       Perl works on a bewildering variety of Unix and Unix-like platforms
       (see e.g. most of the files in the hints/ directory in the source code
       kit).  On most of these systems, the value of $^O (hence $Con-
       fig{'osname'}, too) is determined either by lowercasing and stripping
       punctuation from the first field of the string returned by typing
       "uname -a" (or a similar command) at the shell prompt or by testing the
       file system for the presence of uniquely named files such as a kernel
       or header file.	Here, for example, are a few of the more popular Unix
       flavors:

	   uname	 $^O	    $Config{'archname'}
	   --------------------------------------------
	   AIX		 aix	    aix
	   BSD/OS	 bsdos	    i386-bsdos
	   Darwin	 darwin     darwin
	   dgux 	 dgux	    AViiON-dgux
	   DYNIX/ptx	 dynixptx   i386-dynixptx
	   FreeBSD	 freebsd    freebsd-i386
	   Linux	 linux	    arm-linux
	   Linux	 linux	    i386-linux
	   Linux	 linux	    i586-linux
	   Linux	 linux	    ppc-linux
	   HP-UX	 hpux	    PA-RISC1.1
	   IRIX 	 irix	    irix
	   Mac OS X	 darwin     darwin
	   MachTen PPC	 machten    powerpc-machten
	   NeXT 3	 next	    next-fat
	   NeXT 4	 next	    OPENSTEP-Mach
	   openbsd	 openbsd    i386-openbsd
	   OSF1 	 dec_osf    alpha-dec_osf
	   reliantunix-n svr4	    RM400-svr4
	   SCO_SV	 sco_sv     i386-sco_sv
	   SINIX-N	 svr4	    RM400-svr4
	   sn4609	 unicos     CRAY_C90-unicos
	   sn6521	 unicosmk   t3e-unicosmk
	   sn9617	 unicos     CRAY_J90-unicos
	   SunOS	 solaris    sun4-solaris
	   SunOS	 solaris    i86pc-solaris
	   SunOS4	 sunos	    sun4-sunos

       Because the value of $Config{archname} may depend on the hardware
       architecture, it can vary more than the value of $^O.

       DOS and Derivatives

       Perl has long been ported to Intel-style microcomputers running under
       systems like PC-DOS, MS-DOS, OS/2, and most Windows platforms you can
       bring yourself to mention (except for Windows CE, if you count that).
       Users familiar with COMMAND.COM or CMD.EXE style shells should be aware
       that each of these file specifications may have subtle differences:

	   $filespec0 = "c:/foo/bar/file.txt";
	   $filespec1 = "c:\\foo\\bar\\file.txt";
	   $filespec2 = 'c:\foo\bar\file.txt';
	   $filespec3 = 'c:\\foo\\bar\\file.txt';

       System calls accept either "/" or "\" as the path separator.  However,
       many command-line utilities of DOS vintage treat "/" as the option pre-
       fix, so may get confused by filenames containing "/".  Aside from call-
       ing any external programs, "/" will work just fine, and probably bet-
       ter, as it is more consistent with popular usage, and avoids the prob-
       lem of remembering what to backwhack and what not to.

       The DOS FAT filesystem can accommodate only "8.3" style filenames.
       Under the "case-insensitive, but case-preserving" HPFS (OS/2) and NTFS
       (NT) filesystems you may have to be careful about case returned with
       functions like "readdir" or used with functions like "open" or
       "opendir".

       DOS also treats several filenames as special, such as AUX, PRN, NUL,
       CON, COM1, LPT1, LPT2, etc.  Unfortunately, sometimes these filenames
       won't even work if you include an explicit directory prefix.  It is
       best to avoid such filenames, if you want your code to be portable to
       DOS and its derivatives.  It's hard to know what these all are, unfor-
       tunately.

       Users of these operating systems may also wish to make use of scripts
       such as pl2bat.bat or pl2cmd to put wrappers around your scripts.

       Newline ("\n") is translated as "\015\012" by STDIO when reading from
       and writing to files (see "Newlines").  "binmode(FILEHANDLE)" will keep
       "\n" translated as "\012" for that filehandle.  Since it is a no-op on
       other systems, "binmode" should be used for cross-platform code that
       deals with binary data.	That's assuming you realize in advance that
       your data is in binary.	General-purpose programs should often assume
       nothing about their data.

       The $^O variable and the $Config{archname} values for various DOSish
       perls are as follows:

	    OS		  $^O	   $Config{archname}   ID    Version
	    --------------------------------------------------------
	    MS-DOS	  dos	     ?
	    PC-DOS	  dos	     ?
	    OS/2	  os2	     ?
	    Windows 3.1   ?	     ?		       0      3 01
	    Windows 95	  MSWin32    MSWin32-x86       1      4 00
	    Windows 98	  MSWin32    MSWin32-x86       1      4 10
	    Windows ME	  MSWin32    MSWin32-x86       1      ?
	    Windows NT	  MSWin32    MSWin32-x86       2      4 xx
	    Windows NT	  MSWin32    MSWin32-ALPHA     2      4 xx
	    Windows NT	  MSWin32    MSWin32-ppc       2      4 xx
	    Windows 2000  MSWin32    MSWin32-x86       2      5 00
	    Windows XP	  MSWin32    MSWin32-x86       2      5 01
	    Windows 2003  MSWin32    MSWin32-x86       2      5 02
	    Windows CE	  MSWin32    ?		       3
	    Cygwin	  cygwin     cygwin

       The various MSWin32 Perl's can distinguish the OS they are running on
       via the value of the fifth element of the list returned from
       Win32::GetOSVersion().  For example:

	   if ($^O eq 'MSWin32') {
	       my @os_version_info = Win32::GetOSVersion();
	       print +('3.1','95','NT')[$os_version_info[4]],"\n";
	   }

       There are also Win32::IsWinNT() and Win32::IsWin95(), try "perldoc
       Win32", and as of libwin32 0.19 (not part of the core Perl distribu-
       tion) Win32::GetOSName().  The very portable POSIX::uname() will work
       too:

	   c:\> perl -MPOSIX -we "print join '|', uname"
	   Windows NT|moonru|5.0|Build 2195 (Service Pack 2)|x86

       Also see:

       o   The djgpp environment for DOS, http://www.delorie.com/djgpp/ and
	   perldos.

       o   The EMX environment for DOS, OS/2, etc. emx@iaehv.nl,
	   http://www.leo.org/pub/comp/os/os2/leo/gnu/emx+gcc/index.html or
	   ftp://hobbes.nmsu.edu/pub/os2/dev/emx/  Also perlos2.

       o   Build instructions for Win32 in perlwin32, or under the Cygnus
	   environment in perlcygwin.

       o   The "Win32::*" modules in Win32.

       o   The ActiveState Pages, http://www.activestate.com/

       o   The Cygwin environment for Win32; README.cygwin (installed as perl-
	   cygwin), http://www.cygwin.com/

       o   The U/WIN environment for Win32,
	   http://www.research.att.com/sw/tools/uwin/

       o   Build instructions for OS/2, perlos2

       Mac OS

       Any module requiring XS compilation is right out for most people,
       because MacPerl is built using non-free (and non-cheap!) compilers.
       Some XS modules that can work with MacPerl are built and distributed in
       binary form on CPAN.

       Directories are specified as:

	   volume:folder:file		   for absolute pathnames
	   volume:folder:		   for absolute pathnames
	   :folder:file 		   for relative pathnames
	   :folder:			   for relative pathnames
	   :file			   for relative pathnames
	   file 			   for relative pathnames

       Files are stored in the directory in alphabetical order.  Filenames are
       limited to 31 characters, and may include any character except for null
       and ":", which is reserved as the path separator.

       Instead of "flock", see "FSpSetFLock" and "FSpRstFLock" in the
       Mac::Files module, or "chmod(0444, ...)" and "chmod(0666, ...)".

       In the MacPerl application, you can't run a program from the command
       line; programs that expect @ARGV to be populated can be edited with
       something like the following, which brings up a dialog box asking for
       the command line arguments.

	   if (!@ARGV) {
	       @ARGV = split /\s+/, MacPerl::Ask('Arguments?');
	   }

       A MacPerl script saved as a "droplet" will populate @ARGV with the full
       pathnames of the files dropped onto the script.

       Mac users can run programs under a type of command line interface under
       MPW (Macintosh Programmer's Workshop, a free development environment
       from Apple).  MacPerl was first introduced as an MPW tool, and MPW can
       be used like a shell:

	   perl myscript.plx some arguments

       ToolServer is another app from Apple that provides access to MPW tools
       from MPW and the MacPerl app, which allows MacPerl programs to use
       "system", backticks, and piped "open".

       "Mac OS" is the proper name for the operating system, but the value in
       $^O is "MacOS".	To determine architecture, version, or whether the
       application or MPW tool version is running, check:

	   $is_app    = $MacPerl::Version =~ /App/;
	   $is_tool   = $MacPerl::Version =~ /MPW/;
	   ($version) = $MacPerl::Version =~ /^(\S+)/;
	   $is_ppc    = $MacPerl::Architecture eq 'MacPPC';
	   $is_68k    = $MacPerl::Architecture eq 'Mac68K';

       Mac OS X, based on NeXT's OpenStep OS, runs MacPerl natively, under the
       "Classic" environment.  There is no "Carbon" version of MacPerl to run
       under the primary Mac OS X environment.	Mac OS X and its Open Source
       version, Darwin, both run Unix perl natively.

       Also see:

       o   MacPerl Development, http://dev.macperl.org/ .

       o   The MacPerl Pages, http://www.macperl.com/ .

       o   The MacPerl mailing lists, http://lists.perl.org/ .

       o   MPW, ftp://ftp.apple.com/developer/Tool_Chest/Core_Mac_OS_Tools/

       VMS

       Perl on VMS is discussed in perlvms in the perl distribution.  Perl on
       VMS can accept either VMS- or Unix-style file specifications as in
       either of the following:

	   $ perl -ne "print if /perl_setup/i" SYS$LOGIN:LOGIN.COM
	   $ perl -ne "print if /perl_setup/i" /sys$login/login.com

       but not a mixture of both as in:

	   $ perl -ne "print if /perl_setup/i" sys$login:/login.com
	   Can't open sys$login:/login.com: file specification syntax error

       Interacting with Perl from the Digital Command Language (DCL) shell
       often requires a different set of quotation marks than Unix shells do.
       For example:

	   $ perl -e "print ""Hello, world.\n"""
	   Hello, world.

       There are several ways to wrap your perl scripts in DCL .COM files, if
       you are so inclined.  For example:

	   $ write sys$output "Hello from DCL!"
	   $ if p1 .eqs. ""
	   $ then perl -x 'f$environment("PROCEDURE")
	   $ else perl -x - 'p1 'p2 'p3 'p4 'p5 'p6 'p7 'p8
	   $ deck/dollars="__END__"
	   #!/usr/bin/perl

	   print "Hello from Perl!\n";

	   __END__
	   $ endif

       Do take care with "$ ASSIGN/nolog/user SYS$COMMAND: SYS$INPUT" if your
       perl-in-DCL script expects to do things like "$read = ;".

       Filenames are in the format "name.extension;version".  The maximum
       length for filenames is 39 characters, and the maximum length for
       extensions is also 39 characters.  Version is a number from 1 to 32767.
       Valid characters are "/[A-Z0-9$_-]/".

       VMS's RMS filesystem is case-insensitive and does not preserve case.
       "readdir" returns lowercased filenames, but specifying a file for open-
       ing remains case-insensitive.  Files without extensions have a trailing
       period on them, so doing a "readdir" with a file named A.;5 will return
       a. (though that file could be opened with "open(FH, 'A')").

       RMS had an eight level limit on directory depths from any rooted logi-
       cal (allowing 16 levels overall) prior to VMS 7.2.  Hence
       "PERL_ROOT:[LIB.2.3.4.5.6.7.8]" is a valid directory specification but
       "PERL_ROOT:[LIB.2.3.4.5.6.7.8.9]" is not.  Makefile.PL authors might
       have to take this into account, but at least they can refer to the for-
       mer as "/PERL_ROOT/lib/2/3/4/5/6/7/8/".

       The VMS::Filespec module, which gets installed as part of the build
       process on VMS, is a pure Perl module that can easily be installed on
       non-VMS platforms and can be helpful for conversions to and from RMS
       native formats.

       What "\n" represents depends on the type of file opened.  It usually
       represents "\012" but it could also be "\015", "\012", "\015\012",
       "\000", "\040", or nothing depending on the file organization and
       record format.  The VMS::Stdio module provides access to the special
       fopen() requirements of files with unusual attributes on VMS.

       TCP/IP stacks are optional on VMS, so socket routines might not be
       implemented.  UDP sockets may not be supported.

       The value of $^O on OpenVMS is "VMS".  To determine the architecture
       that you are running on without resorting to loading all of %Config you
       can examine the content of the @INC array like so:

	   if (grep(/VMS_AXP/, @INC)) {
	       print "I'm on Alpha!\n";

	   } elsif (grep(/VMS_VAX/, @INC)) {
	       print "I'm on VAX!\n";

	   } else {
	       print "I'm not so sure about where $^O is...\n";
	   }

       On VMS, perl determines the UTC offset from the "SYS$TIMEZONE_DIFFEREN-
       TIAL" logical name.  Although the VMS epoch began at 17-NOV-1858
       00:00:00.00, calls to "localtime" are adjusted to count offsets from
       01-JAN-1970 00:00:00.00, just like Unix.

       Also see:

       o   README.vms (installed as README_vms), perlvms

       o   vmsperl list, majordomo@perl.org

	   (Put the words "subscribe vmsperl" in message body.)

       o   vmsperl on the web, http://www.sidhe.org/vmsperl/index.html

       VOS

       Perl on VOS is discussed in README.vos in the perl distribution
       (installed as perlvos).	Perl on VOS can accept either VOS- or Unix-
       style file specifications as in either of the following:

	   C<< $ perl -ne "print if /perl_setup/i" >system>notices >>
	   C<< $ perl -ne "print if /perl_setup/i" /system/notices >>

       or even a mixture of both as in:

	   C<< $ perl -ne "print if /perl_setup/i" >system/notices >>

       Even though VOS allows the slash character to appear in object names,
       because the VOS port of Perl interprets it as a pathname delimiting
       character, VOS files, directories, or links whose names contain a slash
       character cannot be processed.  Such files must be renamed before they
       can be processed by Perl.  Note that VOS limits file names to 32 or
       fewer characters.

       Perl on VOS can be built using two different compilers and two differ-
       ent versions of the POSIX runtime.  The recommended method for building
       full Perl is with the GNU C compiler and the generally-available ver-
       sion of VOS POSIX support.  See README.vos (installed as perlvos) for
       restrictions that apply when Perl is built using the VOS Standard C
       compiler or the alpha version of VOS POSIX support.

       The value of $^O on VOS is "VOS".  To determine the architecture that
       you are running on without resorting to loading all of %Config you can
       examine the content of the @INC array like so:

	   if ($^O =~ /VOS/) {
	       print "I'm on a Stratus box!\n";
	   } else {
	       print "I'm not on a Stratus box!\n";
	       die;
	   }

	   if (grep(/860/, @INC)) {
	       print "This box is a Stratus XA/R!\n";

	   } elsif (grep(/7100/, @INC)) {
	       print "This box is a Stratus HP 7100 or 8xxx!\n";

	   } elsif (grep(/8000/, @INC)) {
	       print "This box is a Stratus HP 8xxx!\n";

	   } else {
	       print "This box is a Stratus 68K!\n";
	   }

       Also see:

       o   README.vos (installed as perlvos)

       o   The VOS mailing list.

	   There is no specific mailing list for Perl on VOS.  You can post
	   comments to the comp.sys.stratus newsgroup, or subscribe to the
	   general Stratus mailing list.  Send a letter with "subscribe
	   Info-Stratus" in the message body to majordomo@list.stratagy.com.

       o   VOS Perl on the web at http://ftp.stra-
	   tus.com/pub/vos/posix/posix.html

       EBCDIC Platforms

       Recent versions of Perl have been ported to platforms such as OS/400 on
       AS/400 minicomputers as well as OS/390, VM/ESA, and BS2000 for S/390
       Mainframes.  Such computers use EBCDIC character sets internally (usu-
       ally Character Code Set ID 0037 for OS/400 and either 1047 or POSIX-BC
       for S/390 systems).  On the mainframe perl currently works under the
       "Unix system services for OS/390" (formerly known as OpenEdition),
       VM/ESA OpenEdition, or the BS200 POSIX-BC system (BS2000 is supported
       in perl 5.6 and greater).  See perlos390 for details.  Note that for
       OS/400 there is also a port of Perl 5.8.1/5.9.0 or later to the PASE
       which is ASCII-based (as opposed to ILE which is EBCDIC-based), see
       perlos400.

       As of R2.5 of USS for OS/390 and Version 2.3 of VM/ESA these Unix sub-
       systems do not support the "#!" shebang trick for script invocation.
       Hence, on OS/390 and VM/ESA perl scripts can be executed with a header
       similar to the following simple script:

	   : # use perl
	       eval 'exec /usr/local/bin/perl -S $0 ${1+"$@"}'
		   if 0;
	   #!/usr/local/bin/perl     # just a comment really

	   print "Hello from perl!\n";

       OS/390 will support the "#!" shebang trick in release 2.8 and beyond.
       Calls to "system" and backticks can use POSIX shell syntax on all S/390
       systems.

       On the AS/400, if PERL5 is in your library list, you may need to wrap
       your perl scripts in a CL procedure to invoke them like so:

	   BEGIN
	     CALL PGM(PERL5/PERL) PARM('/QOpenSys/hello.pl')
	   ENDPGM

       This will invoke the perl script hello.pl in the root of the QOpenSys
       file system.  On the AS/400 calls to "system" or backticks must use CL
       syntax.

       On these platforms, bear in mind that the EBCDIC character set may have
       an effect on what happens with some perl functions (such as "chr",
       "pack", "print", "printf", "ord", "sort", "sprintf", "unpack"), as well
       as bit-fiddling with ASCII constants using operators like "^", "&" and
       "|", not to mention dealing with socket interfaces to ASCII computers
       (see "Newlines").

       Fortunately, most web servers for the mainframe will correctly trans-
       late the "\n" in the following statement to its ASCII equivalent ("\r"
       is the same under both Unix and OS/390 & VM/ESA):

	   print "Content-type: text/html\r\n\r\n";

       The values of $^O on some of these platforms includes:

	   uname	 $^O	    $Config{'archname'}
	   --------------------------------------------
	   OS/390	 os390	    os390
	   OS400	 os400	    os400
	   POSIX-BC	 posix-bc   BS2000-posix-bc
	   VM/ESA	 vmesa	    vmesa

       Some simple tricks for determining if you are running on an EBCDIC
       platform could include any of the following (perhaps all):

	   if ("\t" eq "\05")	{ print "EBCDIC may be spoken here!\n"; }

	   if (ord('A') == 193) { print "EBCDIC may be spoken here!\n"; }

	   if (chr(169) eq 'z') { print "EBCDIC may be spoken here!\n"; }

       One thing you may not want to rely on is the EBCDIC encoding of punctu-
       ation characters since these may differ from code page to code page
       (and once your module or script is rumoured to work with EBCDIC, folks
       will want it to work with all EBCDIC character sets).

       Also see:

       o   perlos390, README.os390, perlbs2000, README.vmesa, perlebcdic.

       o   The perl-mvs@perl.org list is for discussion of porting issues as
	   well as general usage issues for all EBCDIC Perls.  Send a message
	   body of "subscribe perl-mvs" to majordomo@perl.org.

       o   AS/400 Perl information at http://as400.rochester.ibm.com/ as well
	   as on CPAN in the ports/ directory.

       Acorn RISC OS

       Because Acorns use ASCII with newlines ("\n") in text files as "\012"
       like Unix, and because Unix filename emulation is turned on by default,
       most simple scripts will probably work "out of the box".  The native
       filesystem is modular, and individual filesystems are free to be case-
       sensitive or insensitive, and are usually case-preserving.  Some native
       filesystems have name length limits, which file and directory names are
       silently truncated to fit.  Scripts should be aware that the standard
       filesystem currently has a name length limit of 10 characters, with up
       to 77 items in a directory, but other filesystems may not impose such
       limitations.

       Native filenames are of the form

	   Filesystem#Special_Field::DiskName.$.Directory.Directory.File

       where

	   Special_Field is not usually present, but may contain . and $ .
	   Filesystem =~ m|[A-Za-z0-9_]|
	   DsicName   =~ m|[A-Za-z0-9_/]|
	   $ represents the root directory
	   . is the path separator
	   @ is the current directory (per filesystem but machine global)
	   ^ is the parent directory
	   Directory and File =~ m|[^\0- "\.\$\%\&:\@\\^\|\177]+|

       The default filename translation is roughly "tr|/.|./|;"

       Note that ""ADFS::HardDisk.$.File" ne 'ADFS::HardDisk.$.File'" and that
       the second stage of "$" interpolation in regular expressions will fall
       foul of the $. if scripts are not careful.

       Logical paths specified by system variables containing comma-separated
       search lists are also allowed; hence "System:Modules" is a valid file-
       name, and the filesystem will prefix "Modules" with each section of
       "System$Path" until a name is made that points to an object on disk.
       Writing to a new file "System:Modules" would be allowed only if "Sys-
       tem$Path" contains a single item list.  The filesystem will also expand
       system variables in filenames if enclosed in angle brackets, so ".Modules" would look for the file "$ENV{'System$Dir'} . 'Mod-
       ules'".	The obvious implication of this is that fully qualified file-
       names can start with "<>" and should be protected when "open" is used
       for input.

       Because "." was in use as a directory separator and filenames could not
       be assumed to be unique after 10 characters, Acorn implemented the C
       compiler to strip the trailing ".c" ".h" ".s" and ".o" suffix from
       filenames specified in source code and store the respective files in
       subdirectories named after the suffix.  Hence files are translated:

	   foo.h	   h.foo
	   C:foo.h	   C:h.foo	  (logical path variable)
	   sys/os.h	   sys.h.os	  (C compiler groks Unix-speak)
	   10charname.c    c.10charname
	   10charname.o    o.10charname
	   11charname_.c   c.11charname   (assuming filesystem truncates at 10)

       The Unix emulation library's translation of filenames to native assumes
       that this sort of translation is required, and it allows a user-defined
       list of known suffixes that it will transpose in this fashion.  This
       may seem transparent, but consider that with these rules
       "foo/bar/baz.h" and "foo/bar/h/baz" both map to "foo.bar.h.baz", and
       that "readdir" and "glob" cannot and do not attempt to emulate the
       reverse mapping.  Other "."'s in filenames are translated to "/".

       As implied above, the environment accessed through %ENV is global, and
       the convention is that program specific environment variables are of
       the form "Program$Name".  Each filesystem maintains a current direc-
       tory, and the current filesystem's current directory is the global cur-
       rent directory.	Consequently, sociable programs don't change the cur-
       rent directory but rely on full pathnames, and programs (and Makefiles)
       cannot assume that they can spawn a child process which can change the
       current directory without affecting its parent (and everyone else for
       that matter).

       Because native operating system filehandles are global and are cur-
       rently allocated down from 255, with 0 being a reserved value, the Unix
       emulation library emulates Unix filehandles.  Consequently, you can't
       rely on passing "STDIN", "STDOUT", or "STDERR" to your children.

       The desire of users to express filenames of the form ".Bar" on
       the command line unquoted causes problems, too: `` command output cap-
       ture has to perform a guessing game.  It assumes that a string
       "<[^<>]+\$[^<>]>" is a reference to an environment variable, whereas
       anything else involving "<" or ">" is redirection, and generally man-
       ages to be 99% right.  Of course, the problem remains that scripts can-
       not rely on any Unix tools being available, or that any tools found
       have Unix-like command line arguments.

       Extensions and XS are, in theory, buildable by anyone using free tools.
       In practice, many don't, as users of the Acorn platform are used to
       binary distributions.  MakeMaker does run, but no available make cur-
       rently copes with MakeMaker's makefiles; even if and when this should
       be fixed, the lack of a Unix-like shell will cause problems with make-
       file rules, especially lines of the form "cd sdbm && make all", and
       anything using quoting.

       "RISC OS" is the proper name for the operating system, but the value in
       $^O is "riscos" (because we don't like shouting).

       Other perls

       Perl has been ported to many platforms that do not fit into any of the
       categories listed above.  Some, such as AmigaOS, Atari MiNT, BeOS, HP
       MPE/iX, QNX, Plan 9, and VOS, have been well-integrated into the stan-
       dard Perl source code kit.  You may need to see the ports/ directory on
       CPAN for information, and possibly binaries, for the likes of: aos,
       Atari ST, lynxos, riscos, Novell Netware, Tandem Guardian, etc.	(Yes,
       we know that some of these OSes may fall under the Unix category, but
       we are not a standards body.)

       Some approximate operating system names and their $^O values in the
       "OTHER" category include:

	   OS		 $^O	    $Config{'archname'}
	   ------------------------------------------
	   Amiga DOS	 amigaos    m68k-amigos
	   BeOS 	 beos
	   MPE/iX	 mpeix	    PA-RISC1.1

       See also:

       o   Amiga, README.amiga (installed as perlamiga).

       o   Atari, README.mint and Guido Flohr's web page
	   http://stud.uni-sb.de/~gufl0000/

       o   Be OS, README.beos

       o   HP 300 MPE/iX, README.mpeix and Mark Bixby's web page
	   http://www.bixby.org/mark/perlix.html

       o   A free perl5-based PERL.NLM for Novell Netware is available in pre-
	   compiled binary and source code form from http://www.novell.com/ as
	   well as from CPAN.

       o   Plan 9, README.plan9

FUNCTION IMPLEMENTATIONS
       Listed below are functions that are either completely unimplemented or
       else have been implemented differently on various platforms.  Following
       each description will be, in parentheses, a list of platforms that the
       description applies to.

       The list may well be incomplete, or even wrong in some places.  When in
       doubt, consult the platform-specific README files in the Perl source
       distribution, and any other documentation resources accompanying a
       given port.

       Be aware, moreover, that even among Unix-ish systems there are varia-
       tions.

       For many functions, you can also query %Config, exported by default
       from the Config module.	For example, to check whether the platform has
       the "lstat" call, check $Config{d_lstat}.  See Config for a full
       description of available variables.

       Alphabetical Listing of Perl Functions


       -X      "-r", "-w", and "-x" have a limited meaning only; directories
	       and applications are executable, and there are no uid/gid con-
	       siderations.  "-o" is not supported.  (Mac OS)

	       "-r", "-w", "-x", and "-o" tell whether the file is accessible,
	       which may not reflect UIC-based file protections.  (VMS)

	       "-s" returns the size of the data fork, not the total size of
	       data fork plus resource fork.  (Mac OS).

	       "-s" by name on an open file will return the space reserved on
	       disk, rather than the current extent.  "-s" on an open filehan-
	       dle returns the current size.  (RISC OS)

	       "-R", "-W", "-X", "-O" are indistinguishable from "-r", "-w",
	       "-x", "-o". (Mac OS, Win32, VMS, RISC OS)

	       "-b", "-c", "-k", "-g", "-p", "-u", "-A" are not implemented.
	       (Mac OS)

	       "-g", "-k", "-l", "-p", "-u", "-A" are not particularly mean-
	       ingful.	(Win32, VMS, RISC OS)

	       "-d" is true if passed a device spec without an explicit direc-
	       tory.  (VMS)

	       "-T" and "-B" are implemented, but might misclassify Mac text
	       files with foreign characters; this is the case will all plat-
	       forms, but may affect Mac OS often.  (Mac OS)

	       "-x" (or "-X") determine if a file ends in one of the exe-
	       cutable suffixes.  "-S" is meaningless.	(Win32)

	       "-x" (or "-X") determine if a file has an executable file type.
	       (RISC OS)

       atan2 Y,X
	       Due to issues with various CPUs, math libraries, compilers, and
	       standards, results for "atan2()" may vary depending on any com-
	       bination of the above.  Perl attempts to conform to the Open
	       Group/IEEE standards for the results returned from "atan2()",
	       but cannot force the issue if the system Perl is run on does
	       not allow it.  (Tru64, HP-UX 10.20)

	       The current version of the standards for "atan2()" is available
	       at .

       atan2   Due to issues with various CPUs, math libraries, compilers, and
	       standards, results for "atan2()" may vary depending on any com-
	       bination of the above.  Perl attempts to conform to the Open
	       Group/IEEE standards for the results returned from "atan2()",
	       but cannot force the issue if the system Perl is run on does
	       not allow it.  (Tru64, HP-UX 10.20)

	       The current version of the standards for "atan2()" is available
	       at .

       binmode Meaningless.  (Mac OS, RISC OS)

	       Reopens file and restores pointer; if function fails, underly-
	       ing filehandle may be closed, or pointer may be in a different
	       position.  (VMS)

	       The value returned by "tell" may be affected after the call,
	       and the filehandle may be flushed. (Win32)

       chmod   Only limited meaning.  Disabling/enabling write permission is
	       mapped to locking/unlocking the file. (Mac OS)

	       Only good for changing "owner" read-write access, "group", and
	       "other" bits are meaningless. (Win32)

	       Only good for changing "owner" and "other" read-write access.
	       (RISC OS)

	       Access permissions are mapped onto VOS access-control list
	       changes. (VOS)

	       The actual permissions set depend on the value of the "CYGWIN"
	       in the SYSTEM environment settings.  (Cygwin)

       chown   Not implemented. (Mac OS, Win32, Plan 9, RISC OS, VOS)

	       Does nothing, but won't fail. (Win32)

       chroot  Not implemented. (Mac OS, Win32, VMS, Plan 9, RISC OS, VOS,
	       VM/ESA)

       crypt   May not be available if library or source was not provided when
	       building perl. (Win32)

	       Not implemented. (VOS)

       dbmclose
	       Not implemented. (VMS, Plan 9, VOS)

       dbmopen Not implemented. (VMS, Plan 9, VOS)

       dump    Not useful. (Mac OS, RISC OS)

	       Not implemented. (Win32)

	       Invokes VMS debugger. (VMS)

       exec    Not implemented. (Mac OS)

	       Implemented via Spawn. (VM/ESA)

	       Does not automatically flush output handles on some platforms.
	       (SunOS, Solaris, HP-UX)

       exit    Emulates UNIX exit() (which considers "exit 1" to indicate an
	       error) by mapping the 1 to SS$_ABORT (44).  This behavior may
	       be overridden with the pragma "use vmsish 'exit'".  As with the
	       CRTL's exit() function, "exit 0" is also mapped to an exit sta-
	       tus of SS$_NORMAL (1); this mapping cannot be overridden.  Any
	       other argument to exit() is used directly as Perl's exit sta-
	       tus. (VMS)

       fcntl   Not implemented. (Win32, VMS)

       flock   Not implemented (Mac OS, VMS, RISC OS, VOS).

	       Available only on Windows NT (not on Windows 95). (Win32)

       fork    Not implemented. (Mac OS, AmigaOS, RISC OS, VOS, VM/ESA, VMS)

	       Emulated using multiple interpreters.  See perlfork.  (Win32)

	       Does not automatically flush output handles on some platforms.
	       (SunOS, Solaris, HP-UX)

       getlogin
	       Not implemented. (Mac OS, RISC OS)

       getpgrp Not implemented. (Mac OS, Win32, VMS, RISC OS, VOS)

       getppid Not implemented. (Mac OS, Win32, RISC OS)

       getpriority
	       Not implemented. (Mac OS, Win32, VMS, RISC OS, VOS, VM/ESA)

       getpwnam
	       Not implemented. (Mac OS, Win32)

	       Not useful. (RISC OS)

       getgrnam
	       Not implemented. (Mac OS, Win32, VMS, RISC OS)

       getnetbyname
	       Not implemented. (Mac OS, Win32, Plan 9)

       getpwuid
	       Not implemented. (Mac OS, Win32)

	       Not useful. (RISC OS)

       getgrgid
	       Not implemented. (Mac OS, Win32, VMS, RISC OS)

       getnetbyaddr
	       Not implemented. (Mac OS, Win32, Plan 9)

       getprotobynumber
	       Not implemented. (Mac OS)

       getservbyport
	       Not implemented. (Mac OS)

       getpwent
	       Not implemented. (Mac OS, Win32, VM/ESA)

       getgrent
	       Not implemented. (Mac OS, Win32, VMS, VM/ESA)

       gethostbyname
	       "gethostbyname('localhost')" does not work everywhere: you may
	       have to use "gethostbyname('127.0.0.1')". (Mac OS, Irix 5)

       gethostent
	       Not implemented. (Mac OS, Win32)

       getnetent
	       Not implemented. (Mac OS, Win32, Plan 9)

       getprotoent
	       Not implemented. (Mac OS, Win32, Plan 9)

       getservent
	       Not implemented. (Win32, Plan 9)

       sethostent
	       Not implemented. (Mac OS, Win32, Plan 9, RISC OS)

       setnetent
	       Not implemented. (Mac OS, Win32, Plan 9, RISC OS)

       setprotoent
	       Not implemented. (Mac OS, Win32, Plan 9, RISC OS)

       setservent
	       Not implemented. (Plan 9, Win32, RISC OS)

       endpwent
	       Not implemented. (Mac OS, MPE/iX, VM/ESA, Win32)

       endgrent
	       Not implemented. (Mac OS, MPE/iX, RISC OS, VM/ESA, VMS, Win32)

       endhostent
	       Not implemented. (Mac OS, Win32)

       endnetent
	       Not implemented. (Mac OS, Win32, Plan 9)

       endprotoent
	       Not implemented. (Mac OS, Win32, Plan 9)

       endservent
	       Not implemented. (Plan 9, Win32)

       getsockopt SOCKET,LEVEL,OPTNAME
	       Not implemented. (Plan 9)

       glob    This operator is implemented via the File::Glob extension on
	       most platforms.	See File::Glob for portability information.

       gmtime  Same portability caveats as localtime.

       ioctl FILEHANDLE,FUNCTION,SCALAR
	       Not implemented. (VMS)

	       Available only for socket handles, and it does what the ioctl-
	       socket() call in the Winsock API does. (Win32)

	       Available only for socket handles. (RISC OS)

       kill    "kill(0, LIST)" is implemented for the sake of taint checking;
	       use with other signals is unimplemented. (Mac OS)

	       Not implemented, hence not useful for taint checking. (RISC OS)

	       "kill()" doesn't have the semantics of "raise()", i.e. it
	       doesn't send a signal to the identified process like it does on
	       Unix platforms.	Instead "kill($sig, $pid)" terminates the
	       process identified by $pid, and makes it exit immediately with
	       exit status $sig.  As in Unix, if $sig is 0 and the specified
	       process exists, it returns true without actually terminating
	       it. (Win32)

       link    Not implemented. (Mac OS, MPE/iX, VMS, RISC OS)

	       Link count not updated because hard links are not quite that
	       hard (They are sort of half-way between hard and soft links).
	       (AmigaOS)

	       Hard links are implemented on Win32 (Windows NT and Windows
	       2000) under NTFS only.

       localtime
	       Because Perl currently relies on the native standard C local-
	       time() function, it is only safe to use times between 0 and
	       (2**31)-1.  Times outside this range may result in unexpected
	       behavior depending on your operating system's implementation of
	       localtime().

       lstat   Not implemented. (VMS, RISC OS)

	       Return values (especially for device and inode) may be bogus.
	       (Win32)

       msgctl
       msgget
       msgsnd
       msgrcv  Not implemented. (Mac OS, Win32, VMS, Plan 9, RISC OS, VOS)

       open    The "|" variants are supported only if ToolServer is installed.
	       (Mac OS)

	       open to "|-" and "-|" are unsupported. (Mac OS, Win32, RISC OS)

	       Opening a process does not automatically flush output handles
	       on some platforms.  (SunOS, Solaris, HP-UX)

       pipe    Very limited functionality. (MiNT)

       readlink
	       Not implemented. (Win32, VMS, RISC OS)

       rename  Can't move directories between directories on different logical
	       volumes. (Win32)

       select  Only implemented on sockets. (Win32, VMS)

	       Only reliable on sockets. (RISC OS)

	       Note that the "select FILEHANDLE" form is generally portable.

       semctl
       semget
       semop   Not implemented. (Mac OS, Win32, VMS, RISC OS, VOS)

       setgrent
	       Not implemented. (Mac OS, MPE/iX, VMS, Win32, RISC OS)

       setpgrp Not implemented. (Mac OS, Win32, VMS, RISC OS, VOS)

       setpriority
	       Not implemented. (Mac OS, Win32, VMS, RISC OS, VOS)

       setpwent
	       Not implemented. (Mac OS, MPE/iX, Win32, RISC OS)

       setsockopt
	       Not implemented. (Plan 9)

       shmctl
       shmget
       shmread
       shmwrite
	       Not implemented. (Mac OS, Win32, VMS, RISC OS, VOS)

       sockatmark
	       A relatively recent addition to socket functions, may not be
	       implemented even in UNIX platforms.

       socketpair
	       Not implemented. (Win32, VMS, RISC OS, VOS, VM/ESA)

       stat    Platforms that do not have rdev, blksize, or blocks will return
	       these as '', so numeric comparison or manipulation of these
	       fields may cause 'not numeric' warnings.

	       mtime and atime are the same thing, and ctime is creation time
	       instead of inode change time. (Mac OS).

	       ctime not supported on UFS (Mac OS X).

	       ctime is creation time instead of inode change time  (Win32).

	       device and inode are not meaningful.  (Win32)

	       device and inode are not necessarily reliable.  (VMS)

	       mtime, atime and ctime all return the last modification time.
	       Device and inode are not necessarily reliable.  (RISC OS)

	       dev, rdev, blksize, and blocks are not available.  inode is not
	       meaningful and will differ between stat calls on the same file.
	       (os2)

	       some versions of cygwin when doing a stat("foo") and if not
	       finding it may then attempt to stat("foo.exe") (Cygwin)

       symlink Not implemented. (Win32, VMS, RISC OS)

       syscall Not implemented. (Mac OS, Win32, VMS, RISC OS, VOS, VM/ESA)

       sysopen The traditional "0", "1", and "2" MODEs are implemented with
	       different numeric values on some systems.  The flags exported
	       by "Fcntl" (O_RDONLY, O_WRONLY, O_RDWR) should work everywhere
	       though.	(Mac OS, OS/390, VM/ESA)

       system  In general, do not assume the UNIX/POSIX semantics that you can
	       shift $? right by eight to get the exit value, or that "$? &
	       127" would give you the number of the signal that terminated
	       the program, or that "$? & 128" would test true if the program
	       was terminated by a coredump.  Instead, use the POSIX W*()
	       interfaces: for example, use WIFEXITED($?) and WEXITVALUE($?)
	       to test for a normal exit and the exit value, WIFSIGNALED($?)
	       and WTERMSIG($?) for a signal exit and the signal.  Core dump-
	       ing is not a portable concept, so there's no portable way to
	       test for that.

	       Only implemented if ToolServer is installed. (Mac OS)

	       As an optimization, may not call the command shell specified in
	       $ENV{PERL5SHELL}.  "system(1, @args)" spawns an external
	       process and immediately returns its process designator, without
	       waiting for it to terminate.  Return value may be used subse-
	       quently in "wait" or "waitpid".	Failure to spawn() a subpro-
	       cess is indicated by setting $? to "255 << 8".  $? is set in a
	       way compatible with Unix (i.e. the exitstatus of the subprocess
	       is obtained by "$? >> 8", as described in the documentation).
	       (Win32)

	       There is no shell to process metacharacters, and the native
	       standard is to pass a command line terminated by "\n" "\r" or
	       "\0" to the spawned program.  Redirection such as "> foo" is
	       performed (if at all) by the run time library of the spawned
	       program.  "system" list will call the Unix emulation library's
	       "exec" emulation, which attempts to provide emulation of the
	       stdin, stdout, stderr in force in the parent, providing the
	       child program uses a compatible version of the emulation
	       library.  scalar will call the native command line direct and
	       no such emulation of a child Unix program will exists.  Mileage
	       will vary.  (RISC OS)

	       Far from being POSIX compliant.	Because there may be no under-
	       lying /bin/sh tries to work around the problem by forking and
	       execing the first token in its argument string.	Handles basic
	       redirection ("<" or ">") on its own behalf. (MiNT)

	       Does not automatically flush output handles on some platforms.
	       (SunOS, Solaris, HP-UX)

	       The return value is POSIX-like (shifted up by 8 bits), which
	       only allows room for a made-up value derived from the severity
	       bits of the native 32-bit condition code (unless overridden by
	       "use vmsish 'status'").	For more details see "$?" in perlvms.
	       (VMS)

       times   Only the first entry returned is nonzero. (Mac OS)

	       "cumulative" times will be bogus.  On anything other than Win-
	       dows NT or Windows 2000, "system" time will be bogus, and
	       "user" time is actually the time returned by the clock() func-
	       tion in the C runtime library. (Win32)

	       Not useful. (RISC OS)

       truncate
	       Not implemented. (Older versions of VMS)

	       Truncation to zero-length only. (VOS)

	       If a FILEHANDLE is supplied, it must be writable and opened in
	       append mode (i.e., use "open(FH, '>>filename')" or
	       "sysopen(FH,...,O_APPEND|O_RDWR)".  If a filename is supplied,
	       it should not be held open elsewhere. (Win32)

       umask   Returns undef where unavailable, as of version 5.005.

	       "umask" works but the correct permissions are set only when the
	       file is finally closed. (AmigaOS)

       utime   Only the modification time is updated. (BeOS, Mac OS, VMS,
	       RISC OS)

	       May not behave as expected.  Behavior depends on the C runtime
	       library's implementation of utime(), and the filesystem being
	       used.  The FAT filesystem typically does not support an "access
	       time" field, and it may limit timestamps to a granularity of
	       two seconds. (Win32)

       wait
       waitpid Not implemented. (Mac OS, VOS)

	       Can only be applied to process handles returned for processes
	       spawned using "system(1, ...)" or pseudo processes created with
	       "fork()". (Win32)

	       Not useful. (RISC OS)

Supported Platforms
       As of September 2003 (the Perl release 5.8.1), the following platforms
       are able to build Perl from the standard source code distribution
       available at http://www.cpan.org/src/index.html

	       AIX
	       BeOS
	       BSD/OS	       (BSDi)
	       Cygwin
	       DG/UX
	       DOS DJGPP       1)
	       DYNIX/ptx
	       EPOC R5
	       FreeBSD
	       HI-UXMPP        (Hitachi) (5.8.0 worked but we didn't know it)
	       HP-UX
	       IRIX
	       Linux
	       LynxOS
	       Mac OS Classic
	       Mac OS X        (Darwin)
	       MPE/iX
	       NetBSD
	       NetWare
	       NonStop-UX
	       ReliantUNIX     (formerly SINIX)
	       OpenBSD
	       OpenVMS	       (formerly VMS)
	       Open UNIX       (Unixware) (since Perl 5.8.1/5.9.0)
	       OS/2
	       OS/400	       (using the PASE) (since Perl 5.8.1/5.9.0)
	       PowerUX
	       POSIX-BC        (formerly BS2000)
	       QNX
	       Solaris
	       SunOS 4
	       SUPER-UX        (NEC)
	       SVR4
	       Tru64 UNIX      (formerly DEC OSF/1, Digital UNIX)
	       UNICOS
	       UNICOS/mk
	       UTS
	       VOS
	       Win95/98/ME/2K/XP 2)
	       WinCE
	       z/OS	       (formerly OS/390)
	       VM/ESA

	       1) in DOS mode either the DOS or OS/2 ports can be used
	       2) compilers: Borland, MinGW (GCC), VC6

       The following platforms worked with the previous releases (5.6 and
       5.7), but we did not manage either to fix or to test these in time for
       the 5.8.1 release.  There is a very good chance that many of these will
       work fine with the 5.8.1.

	       DomainOS
	       Hurd
	       MachTen
	       PowerMAX
	       SCO SV
	       Unixware
	       Windows 3.1

       Known to be broken for 5.8.0 and 5.8.1 (but 5.6.1 and 5.7.2 can be
       used):

	       AmigaOS

       The following platforms have been known to build Perl from source in
       the past (5.005_03 and earlier), but we haven't been able to verify
       their status for the current release, either because the hardware/soft-
       ware platforms are rare or because we don't have an active champion on
       these platforms--or both.  They used to work, though, so go ahead and
       try compiling them, and let perlbug@perl.org of any trouble.

	       3b1
	       A/UX
	       ConvexOS
	       CX/UX
	       DC/OSx
	       DDE SMES
	       DOS EMX
	       Dynix
	       EP/IX
	       ESIX
	       FPS
	       GENIX
	       Greenhills
	       ISC
	       MachTen 68k
	       MiNT
	       MPC
	       NEWS-OS
	       NextSTEP
	       OpenSTEP
	       Opus
	       Plan 9
	       RISC/os
	       SCO ODT/OSR
	       Stellar
	       SVR2
	       TI1500
	       TitanOS
	       Ultrix
	       Unisys Dynix

       The following platforms have their own source code distributions and
       binaries available via http://www.cpan.org/ports/

				       Perl release

	       OS/400 (ILE)	       5.005_02
	       Tandem Guardian	       5.004

       The following platforms have only binaries available via
       http://www.cpan.org/ports/index.html :

				       Perl release

	       Acorn RISCOS	       5.005_02
	       AOS		       5.002
	       LynxOS		       5.004_02

       Although we do suggest that you always build your own Perl from the
       source code, both for maximal configurability and for security, in case
       you are in a hurry you can check http://www.cpan.org/ports/index.html
       for binary distributions.

SEE ALSO
       perlaix, perlamiga, perlapollo, perlbeos, perlbs2000, perlce, perlcyg-
       win, perldgux, perldos, perlepoc, perlebcdic, perlfreebsd, perlhurd,
       perlhpux, perlirix, perlmachten, perlmacos, perlmacosx, perlmint,
       perlmpeix, perlnetware, perlos2, perlos390, perlos400, perlplan9, per-
       lqnx, perlsolaris, perltru64, perlunicode, perlvmesa, perlvms, perlvos,
       perlwin32, and Win32.

AUTHORS / CONTRIBUTORS
       Abigail , Charles Bailey ,
       Graham Barr , Tom Christiansen ,
       Nicholas Clark , Thomas Dorner ,
       Andy Dougherty , Dominic Dunlop , Neale Ferguson , David J. Fiander
       , Paul Green , M.J.T. Guy
       , Jarkko Hietaniemi , Luther Huffman
       , Nick Ing-Simmons ,
       Andreas J. Koenig , Markus Laker , Andrew M. Langmead , Larry Moore
       , Paul Moore ,
       Chris Nandor , Matthias Neeracher ,
       Philip Newton , Gary Ng <71564.1743@CompuServe.COM>, Tom
       Phoenix , Andre Pirard ,
       Peter Prymmer , Hugo van der Sanden
       , Gurusamy Sarathy , Paul
       J. Schinder , Michael G Schwern , Dan Sugalski , Nathan Torkington
       .



perl v5.8.8			  2006-01-07			   PERLPORT(1)